CDMA methods (CDMA stands for code division multiple access) are standard transmission methods in satellite and mobile radio telephone systems for the radio interface between a transmission means and a reception means. CDMA methods are thereby band spread methods (spread spectrum) wherein a narrow-band useful signal is spectrally spread by a usually whole-number factor using a spread code and receives a noise-like characteristic. For unintended receivers, the band-spread signal represents additional noise that is additively overlaid on the useful signals from other transmission equipment. However, an intentional disturbance of the band-spread signal can also be opposed.
In standard CDMA receivers, the reception signal is despread or, respectively correlated with the spread code of the transmission means. A narrow-band jammer is spectrally spread by the despreading, so that its interfering effect is reduced by low-pass filtering.
The broadband transmission via the radio interface enables the reception means to resolve significantly more multi-path paths than would be possible given a narrow-band transmission. The transmission ensues at the same time for a plurality of connections and with the same carrier frequency. In a mobile radio telephone network, thus, a plurality of base stations can simultaneously maintain connections to a mobile station. Further improvements in the quality of the connection can thus be achieved.
This complexity of the reception conditions at the reception station with, usually, a plurality of propagation paths, with disturbances between the individual, transmitted symbols and with interference of further connections of the same carrier frequency, as well as noise disturbances, makes the separate interpretation of the parts for the useful signal and for the noise signals more difficult.
It is known to implement the measurement of the noise power using a reference channel. The reference channel is established either in a neighboring frequency band or, separated from the useful signals on the basis of time-division multiplex, in the same frequency band. However, only the thermal noise part of the disturbances can be identified with such a method, so that only an imprecise determination of the noise part is achieved for the CDMA method.